Electric discharge device



April 1940- A. c. THOMPSON 2,196,040

ELECTRIC DISCHARGE DEVICE Filed March 14, 1936 2/ 1 I g e 1 F I lNlENTOR By AC. THOMPSON 04ml? M A TTORNEV Patented Apr. 2, 1940 UNITEDSTATES ELECTRIC DISCHARGE DEVICE Albert 0. Thompson, Mount Vernon, N.Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Application March 14, 1936,'Serial No.68,875

3 Claims.

This invention relates to electric discharge devices, and, moreparticularly, to those of the gasfilled type.

One of the difilculties which has been encountered with gas-filledelectric discharge devices or tubes is that the devices are irreparablydamaged if the anode potential is applied before the cathode temperaturehas reached a sufficiently high value. Present practices for overcomingthis condition consist of auxiliary circuits employing timing devices,such as thermal relays or condenser delay circuits, which delay theapplication of the anode potential for a predetermined time aftercathode heating current has been applied. To afford complete protection,this interval must be long enough to safeguard a tube starting fromnormal or cold condition, and unless special arrangements are providedto reduce this period when only a momentary interruption of power occursand the cathode does not cool to any great extent, considerable time iswasted. In addition, several relays are generally required and the wholecontrol mechanism is relatively expensive.

An object of this invention is to overcome these difficulties by animprovement in the construction of the gas-filled tube itself.

A feature of this invention comprises a gasfilled tube having athermionic cathode, an anode, an auxiliary electrode and means definingseparate chambers for the anode and auxiliary electrode with the cathodein each.

Another feature comprises a gas-filled tube having a plurality of anodesin separate chambers.

A further feature comprises the combination of a gas-filled electricdischarge device comprising a thermionic cathode and a plurality ofanodes in separate chambers, and means in the circuit of the cathode andone anode for applying potential toanother anode when the cathode hasreached a predetermined temperature.

Still another feature comprises a gas-filled tube comprising athermionic cathode and a plurality of anodes separated by a positive ionshield or partition.

Other and further features will be apparent from the descriptive matterwhich follows hereinafter.

A more complete understanding of the invention will be obtained from thedetailed description which follows, taken in conjunction with theappended drawing, wherein:

Figure 1 is a cross-sectional view of an electric discharge deviceembodying the invention;

Fig. 2 is a cross-sectional view of another discharge device embodying.this invention; and

Fig. 3 shows a circuit embodying the device of either Fig. 1 or Fig. 2.

Fig. 1 discloses an electric discharge device 10. It comprises anenvelope, enclosure or vessel ll, preferably filled with an inert gas orvapor such as argon, neon, mercury or mixture thereof. The envelope maybe of transparent vitreous material, having a reversely and inward-1yprojecting portion or stem l2 including a press 13. vessel and supportedon the press by sealed leading-in conductors l4, 65, I6, H and I8 are acontrol electrode or helical grid 59, an indirectly heated cathode orfilament 2d, a main anode or anodes 2! electrically connected by theconductorv 35, and a heater filament 22 embedded in an insulatingmaterial '35 surrounded by the cathode, which maybe cylindrical inshape. At the end 23 of the vessel opposite the stem is supported anauxiliary electrode or anode 24 having a supporting, leading-inconductor 1 25 projecting through and sealed in the envelope, andterminated on a terminal cap or member 26. A partition, wall, disc orshield member 21, planar and circular in shape, preferably impervious topositive ions, and, for example, ofmetal, divides the vessel interiorinto two chambers 28, 29 and has a central aperture through which theupper end. portion 36 of the cathode extends into the chamber containingthe auxiliary electrode.

tween the shield and the cathode need not be gas-tight but should bereasonably close fitting so as to prevent the passage of positive ions.Suitable supporting rods or struts 33 support the shield from the stem.A connection 34 between the shield and cathode obviates any need forterminating the shield support at a separate terminal, which arrangementwould require insulation between the shield and the cathode, although,if desired, the shield support may be brought out to a separate terminalto be grounded or to be maintained ata desired potential.

Fig. 2 discloses an electric discharge device 40, preferably filled withan inert gas or vapor, such as argon, neon, mercury or a mixturethereof, similar to the'de'vice of Fig. 1, like parts being designatedby like numerals. The positive ion shield, howevenis provided by anenclosure, shell or box member 4i, cylindrical in shape, comprising acasing i2 and a cover portion :83 which divides the vessels interiorinto chambers M, 25. The shell M is supported by the rod 3E, andcontains an aperture through which extends the end portion 30 of thecathode. The joints 45, 46

between the casing 42. and cover 43 and the oath Within the The jointsSi, 32 between the shield and the vessel or be- I ode and the shell neednot be gas-tight, but, preferably, are sufliciently close fitting toprevent the passage of positive ions. The auxiliary electrode or anode24 is positioned within the chamber 44, and may be supported therein bythe leading-in conductor 4'1, the portion of which between the press andthe anode 24 is enclosed in suitable insulation 48, which may be glassor ceramic tubing.

The device of either Fig. 1 or Fig. 2 may be embodied in a signal orpulse transferring or transmitting circuit, as is shown in Fig. 3, inwhich a signal or pulse is to be transferred from incoming line L tooutgoing line 0, or line L is to control line 0. The electric dischargedevice A is either the device or 4D. The cathode is connected through aresistance 50 to ground, and the heater element or filament is shownprovided in circuit with a battery as a source of heating current. Themain anode is connected by conductor 52 with the armature 53 of relay54, the winding of which is connected by conductor 55 in series with theauxiliary electrode and battery 56 to ground. The grid is connectedthrough a protective resistance 58 and conductor 51 to the back armature59 of line relay G0 and through the back contact of armature 59 andresistance 6| to ground. A condenser 62 is in shunt with the grid. Thefront contact of armature 59 is connected through a resistance 53 tobattery 64 and ground, and the front armature 65 of relay 6% to battery68 and ground. The winding of relay 6'! is connected through conductors6B, 69 with the contacts associated with arrnatures 65,

. 53, respectively. The conductors comprising line 0 are connected withthe armature T0 and its associated contact.

Energization or" the heater element by closure of the switch H causesthe cathode to begin to emit electrons with a resultant current flow inthe cathode-auxiliary electrode circuit and through relay 54, thecircuit being from ground, battery 58, winding of relay 54, conductor55, anode 24, cathode 20, resistance Bil to ground. The constants of thecircuit are so proportioned that the relay does not get sufficientcurrent to operate until the cathode has reached its safe operatingtemperature. When this occurs, relay 5% operates, the armature 53engaging with its associated contact and connecting the main anodethrough the winding of relay 6'! to the contact associated with thearmature 65. Of course, when relay 60 operates armature 65 engages withits contact to apply the normal operating potential to the main anode.To avoid the production of positive ions and the resultant deteriorationof the oathode in the chamber 28 or 44, a much lower voltage is appliedto the auxiliary anode than to the main anode. The auxiliary anodepotential might be of the order of 24-48 volts, as compared withapproximately 150 volts for the main anode in a typical device. If,after the circuit for application of main anode potential has beencompleted, there is a loss of cathode emission, resulting, for example,from a failure of the heater power, the current in the cathode-auxiliaryelectrode circuit will decrease to a point where relay 54 releases andthe voltage on the main anode is removed before any damage to thecathode occurs. Upon the restoration of the heater power, the current inthe auxiliary circuit rises as the temperature of the cathode rises,and, when the safe value is reached, the main anode potential is againapplied, assuming relay 50 to be already operated. The time for thedischarge device to again become operative is dependent on the amountthe temperature has dropped, and is only the minimum required to protectthe device under these conditions rather than a predetermined intervalbased on starting cold.

The purpose of the positive ion shield 21 or Al is to keep the ionsgenerated in the main portion 29 of the tube from entering the spacearound the auxiliary electrode, where their presence would prevent thatelectrode from maintaining close control of the current in thecathodeauxiliary electrode circuit. If ionization were allowed to takeplace in this portion of the device, to the same extent as in the mainportion, the current in relay 55 would remain at a high value for toolong a period and the relay would not release soon enough to protect thecathode.

Referring again to Fig. 3, and assuming that the cathode is at itspredetermined or operating temperature and relay 5G operated with itsarmature in engagement with its associated contact, relay G! will notoperate because the voltage on the grid is too low to permit the deviceto ionizc or fire, even though a signal or pulse arriving over line Lhas caused relay 6'5 to operate, thereby having caused armature 65 toengage with its associated contact. Operation of relay 51; causesarmature 59 to engage with its associated front contact to applypotential from battery 64 through resistance 83 to the condenser 62 andthence to the grid through the protective resistance 58. At the momentrelay 66 operates, the voltage across condenser $2 is essentially zero,but it rises as the charge on the condenser increases. The potential onthe grid rises at the same time, and when the critical value is reachedthe device ionizes or fires, a conducting path between the cathode andmain anode being established to complete the following circuit: ground,battery 66, armature 65, conductor 68, winding of relay 6?, conductor69, armature 53, conductor 52, anode 2i, cathode 2i resistance 50 toground. Relay 61 operates, causing armature ill to engage with itsassociated contact to close a circuit through the outgoing line D, thecircuit remaining closed so long as the relay Ed is energized and thereis no failure of the device or tube A. The time required for the deviceto fire is that required for the voltage on the condenser and on thegrid to rise to the critical value, and is determined by the potentialof battery 64, the capacity of the condenser, and the value of theresistance 63. Resistance 58 supplies a biasing potential to the gridduring the time the circuit is in non-operated condition, i. e., whenrelay 60 is deenergized, while resistance Bl serves the dual purpose ofconnecting this potential to the grid and of limiting the dischargecurrent of the condenser upon the release of relay 60. The potential forthe main anode is supplied through a contact under control of relay 6!)so that when the latter releases, the potential is removed. This isnecessary because of the act that with gasfilled devices or tubes thegrid loses control upon ionization, and the discharge will not stopunless the anode potential is reduced below the sustaining value whichis much lower than the starting value.

While this invention has been disclosed with reference to variousspecific embodiments thereof, it is to be understood that it is notlimited thereto, but by the scope of the appended claims only.

What is claimed is:

1. An electric discharge device comprising a gas-filled enclosingvessel, a thermionic cathode, a control electrode, a main anode, anauxfliary anode opposite a. relatively small portion of said cathode,and an enclosure within said vessel completely surrounding saidauxiliary anode and said relatively small portion of said cathode.

2. An electric discharge device comprising a gas-filled enclosingvessel, a thermionic cathode, acontrol electrode, a main anode, anauxiliary anode, opposite one end portion of said cathode, and a solidwalled housing within said vessel and supported in part by said cathode,said housing having an opening into which said end portion extends, andcompletely enclosing said auxiliary anode and said end portion.

3. An electric discharge device comprising an enclosing vessel having afilling of gas, a. positive ion shield dividing said vessel into twochambers, a cathode having a large area electron emitting surface in oneof said chambers and a restricted electron emitting portion in the otherof said chambers, an auxiliary anode in said other chamher and inproximity to said portion whereby a small potential between saidauxiliary anode and said portion sufiices for ionization of the gaptherebetweemand a main anode in cooperative relation with said surfaceand relatively remote therefrom. I

ALBERT C. THOMPSON.

